1. Field of the Invention
The present invention relates to a fingerprint registering method for registering a fingerprint by judging whether or not it has been registered and to a fingerprint checking device.
The present invention relates to a fingerprint registering method with security improved and to a fingerprint checking entrance/exit control system.
The present invention relates to a fingerprint checking method for extracting a fingerprint in the direction of ridge lines in registering and checking the fingerprint.
The present invention relates to a fingerprint checking method for checking a registered fingerprint and an affixed fingerprint to authenticate personal identification.
The present invention relates to a fingerprint checking entrance/exit control system for checking an affixed fingerprint and a registered fingerprint to control the permission or not of entrance.
The present invention relates to a fingerprint checking device for checking a registered fingerprint and an affixed fingerprint.
The present invention relates to a fingerprint registering method for a fingerprint checking device.
2. Prior Art
Fingerprint checking devices which check a registered fingerprint with an affixed fingerprint to authenticate personal identification have been put into practical use. And, the fingerprint checking devices are desired to easily register fingerprints with reliability.
As shown in FIG. 30, a conventional way of registering fingerprints judges whether or not fingerprinting for a fingerprint image pickup is for the first time (D1), if it is its first time, temporarily registers it (D2), if not its first time, judges whether or not it is the second time (D3), if it is its second time of fingerprinting, checks the temporarily registered fingerprint with the second affixed fingerprint (D4), judges whether or not they match (D5), if they match, formally registers (D6), and terminates normally. And, if they do not match, it is concluded as registration failure. In this case, registration processing can be repeated on another finger.
After binarizing a fingerprint shown in FIG. 31 (A), it is thinning-processed as shown in (B), and a registering window in a square frame is enlarged as shown in (C). In (C), N indicates a normal minutia, and P1 to P4 indicate pseudo minutiae. For example, a bifurcation point having a bifurcation length of a prescribed length of a ridge line and an ending point having a space of a prescribed length or more are determined as normal minutia, and a bifurcation point and an ending point under other conditions are determined as pseudo minutia.
In the above-described temporary registering and formal registering, registering windows each consisting of, for example, 36.times.30 picture elements with normal minutia N at almost the center is selected in the number of about 15 for example from a single fingerprint image and registered as shown in FIG. 31 (C).
Since fingerprints do not change, they are suitable for authenticating personal identification. And, a registered fingerprint and an affixed fingerprint are checked by a fingerprint checking device, and when they match, the pertinent fingerprint is judged as of a registered person. But, the fingerprint image pictured by a fingerprint image pickup unit changes largely depending on chaps, wrinkles, dirt and a fingerprinting pressure of a finger tip. Therefore, checking immediately after the temporary registering mostly results in matching, but there is a disadvantage that a matching rate is lowered sharply with a lapse of time.
FIG. 32 and FIG. 33 are explanatory diagrams of fingerprint images and thinning-processed images. (A) in the respective drawings shows pictured fingerprint images, and (B) shows images obtained by binarizing and thinning processing, and rectangles indicate registering windows. In FIG. 32, the fingerprint image is relatively good, and normal minutiae are easily extracted as shown in (B). But, in FIG. 33, the fingerprint has chaps and many pseudo minutiae as shown in (B), so that it is not easy to select registering windows.
The fingerprint shown in FIG. 33 is formally registered because it has a high possibility of matching when it is checked with a registered fingerprint immediately after the temporary registering. But, the states of chaps and wrinkles change with a lapse of time, and a match rate is sharply lowered accordingly. To avoid it, it is desirable to obtain a fingerprint image with good image quality as shown in FIG. 32, but it is hard to judge whether or not the fingerprint image is good at the time of registering a fingerprint excepting when the fingerprint image is heavily deteriorated such that mismatching results. Therefore, even when another finger is used to register a fingerprint in case of mismatching, it is impossible to judge which finger is best.
On the other hand, there is a known fingerprint checking entrance/exit control system which authenticates personal identification by fingerprint checking to allow the entrance or exit. It is demanded to improve the security of fingerprint registration in such a system.
FIG. 34 is an explanatory diagram of a system, in which reference numeral 261 denotes a fingerprint registering device, 262 a fingerprint checking unit consisting of a host computer, 263 a modem, 264 a private branch exchange (PBX), 265-1 to 265-n rooms such as an office, a computer room and a vault, 266-1 to 266-n fingerprint checking gates, and 267-1 to 267-n electric locks.
The electric locks 267-1 to 267-n are for unlocking the doors to the rooms 265-1 to 265-n, and the fingerprint checking gates 266-1 to 266-n are provided to correspond to the rooms 265-1 to 265-n and connected to the fingerprint checking unit through the private branch exchange 264. And, in a case of a small-scale fingerprint checking entrance/exit control system, the private branch exchange 264 and the modem 263 may be omitted, and the fingerprint checking gates 266-1 to 266-n and the fingerprint checking unit 262 can be connected by an LAN or the like.
The fingerprint checking gates 266-1 to 266-n each have a fingerprinting part, and read the affixed fingerprint to transfer to the fingerprint checking unit 262. The fingerprint checking unit 262 checks the fingers registered in the fingerprint registering device 261 with the transferred fingerprint, and transfers the checked result to the fingerprint checking gates through the private branch exchange 264. Otherwise, the fingerprint data registered in the fingerprint registering device 261 is transferred to the fingerprint checking gates 266-1 to 266-n to store in a storage device (not shown), a fingerprint checking unit similar to the fingerprint checking unit 262 is provided at the respective fingerprint checking gates 266-1 to 266-n, and the registered fingerprints can be checked with the affixed fingerprint at the respective fingerprint checking gates 266-1 to 266-n.
And, when the registered fingerprint matches with the affixed fingerprint, the fingerprint checking gate unlocks the electric lock to allow entrance, but when they do not match, the electric lock is not unlocked to prohibit the entrance. And, when the use of a computer is allowed by fingerprint checking, the computer can be used when the registered fingerprint matches with the affixed fingerprint and the electric lock is unlocked.
Therefore, a person who has registered his or her fingerprint can enter a room or use a computer without using an ordinary key when personal identification is authenticated by fingerprint checking. In such a case, by registering a fingerprint and a room as a pair, only specified persons are allowed to enter a specified room. And, it is possible to register a specified person to enter every room.
By registering the fingerprints of persons allowed to enter a room in the fingerprint registering device 261, only fingerprint registered persons can enter the room. To register a fingerprint, it is often that registering is permitted according to a password, or registering is allowed by using a registering key.
But, it is highly possible that a password is used by stealth unless its number of digits is increased, but when the number of digits is increased, it is troublesome to enter the password. And, in the case of using the registering key, there is a disadvantage that any person can register his or her fingerprint by using the registering key. Accordingly, the security of entrance to or exit from a room after registering a fingerprint can be retained fully, but the security at the time of registering a fingerprint is not sufficient. And, fingerprint checking to authenticate personal identification is to check an affixed fingerprint with a previously registered fingerprint, and it is generally configured that to register a fingerprint, minutiae of a fingerprint image obtained by picturing an affixed fingerprint are extracted as registered fingerprint data, the registered fingerprint data is stored in a file, and the affixed fingerprint image is binarized at the time of fingerprint checking and checked with the registered fingerprint data read from the file. To extract the minutiae, the fingerprint image is required to accurately show the ridge lines of the fingerprint, and various types of image processing methods have been proposed.
FIG. 35 is an explanatory view of a fingerprint checking device, in which reference 311 denotes a fingerprint image pickup unit, 312 a multivalued image capturing unit, 313 a fingerprinting judging unit, 314 a ridge line direction detecting unit, 315 a spatial filter, 316 a binarizing unit, 317 a minutia extracting unit, 318 a registering unit, and 319 a checking unit. The fingerprint image pickup unit 311 takes a picture of an affixed fingerprint by a CCD camera, the multivalued image capturing unit 312 converts an analog image into a multivalued digital image and stores in an image memory (not shown), and the fingerprinting judging unit 313 judges whether or not a fingerprint has been affixed based on the multivalued image.
At the time of registering a fingerprint, the fingerprint is affixed and pictured by the fingerprint image pickup unit 311, and captured as a multivalued image by the multivalued image capturing unit 312. Based on the multivalued image, it is judged by the fingerprinting judging unit 313 whether fingerprinting has been made or not, and when it is judged as fingerprinting, the multivalued image is binarized by the ridge line direction detecting unit 314. For example, with 16.times.16 picture elements as one block, division into respective blocks is made, the ridge line direction is detected for each block, and conversion into the multivalued image is made by the spatial filter 315. The spatial filter 315 determines a luminance average value of focused picture elements and multiple picture elements in the ridge line direction on a multivalued image captured by the multivalued image capturing unit 312, for example, and processing of determining the luminance of the focused picture element can be made with respect to the blocks.
The multivalued image processed by the spatial filter 315 is binarized in the binarizing unit 316, and based on the binarized image, minutiae such as bifurcation points of ridge lines are extracted in a prescribed number by the minutia extracting unit, and data containing the minutiae is stored as registered fingerprint data in the registering unit 318.
In checking a fingerprint, the fingerprint is affixed and pictured by the fingerprint image pickup unit 311, and captured as a multivalued image by the multivalued image capturing unit 312. Based on the multivalued image, it is judged by the fingerprinting judging unit 313 whether fingerprinting has been made or not, and when it is judged as fingerprinting, the multivalued image is binarized by the binarizing unit 316, the binarized image of fingerprint is checked with the registered fingerprint data read from the registering unit 318 by the checking unit 319, and a checked result output signal on matching or mismatching is sent to an unillustrated gate having an electric lock.
FIG. 36 is an explanatory diagram of dividing a pictured image into blocks, and when 512.times.512 picture elements are determined as one screen, division into 1024 blocks is made with 16.times.16 picture elements as one block, for example. And, P.sub.1.1.about.P.sub.1.256 denote the picture elements in the top left block, and P.sub.1024.1.about.P.sub.1024.256 denote the picture elements in the right bottom.
FIG. 37 is an explanatory diagram of judging the direction of picture elements. In the ridge line direction detecting unit 314 shown in FIG. 35, using a 3.times.3 picture element direction detecting mask and a pattern with its center as the focused picture element, the directions of the focused picture elements are determined as shown in D1 to D8. For example, pattern 1-1 and pattern 1-2 are judged as the same horizontal direction D1, and pattern 3-1 and pattern 3-2 are judged as the same 45-degree direction D3. And, if not belonging to 16 types of direction detecting mask patterns shown in FIG. 37, the direction of focused picture elements does not belong to any pattern. Therefore, the focused picture elements can be judged to belong to which of the eight directions D1 to D8 in this case, they will be one of eight directions indicated by 1 to 8 at right bottom of the drawing. And, each block is determined to have a direction that the number of picture elements in every direction in the block is maximum as the ridge line direction of the pertinent block.
FIG. 38 is a flowchart of a conventional example, in which a block number is initialized with m=1 (B-1). In other words, number m for 1 to 1024 is allocated with respect to 1024 blocks in the image shown in FIG. 36, and the block number m is determined as 1 for initialization. Then, with n=1 (B2), the picture element number n in the block is initialized. In other words, the number n for 256 picture elements in the image shown in FIG. 36 is allocated, and this picture element number n is determined as 1 for initialization.
Then, contents V1 to V8 of a totaling register for totaling the number of picture elements corresponding to respective directions 1 to 8 shown at the lower right of FIG. 37 are cleared to zero and initialized (B3). And, the direction of picture element P.sub.m.n (m=) 1.about.1024, n=1.about.256) is detected by using a direction detecting mask as described in connection with FIG. 37, +1 is added to Vx (x=1.about.8) corresponding to a matched direction (B4). And, it is judged whether or not n=256 (B5), and if n is not equal to 256, it is determined as n=n+1 (B6), then processing goes to step (B4). The above-described steps (B2) to (B6) correspond to histogram generation processing according to the direction in the block.
When n=256, processing on one block is completed, and it is determined as i=1 (B7), register No. i according to the direction is initialized, it is determined as Sm=0 (B8), and a direction component maximum value Sm is initialized. And, totaling register Vi and the maximum value Sm are compared to judge whether Sm&lt;Vi (B9), and when Sm&lt;Vi, it is determined as Sm=Vi (B10), and Dm=i (B11). In other words, the totaling register Vi is determined as the maximum value Sm, and direction No. i of the totaling register Vi is determined as direction No. Dm of the maximum value Sm.
When Sm is not smaller than Vi, or after step (B11), it is judged whether or not i=8 (B12). In other words, it is judged whether or not processing has been made on eight directions, and when i is not equal to 8, it is determined as i=i+1 (B14), and processing goes to step (B5). And, when i=8, it is judged whether or not m=1024 (B13). Namely, it is judged whether or not processing on all blocks has been completed, and if not completed, it is determined as m=m +1 (B15). And, block No. m is determined as an increment, and processing goes to step (B2). Therefore, at the end of processing, the maximum value Sm of the direction component of respective blocks is stored in a direction component maximum value storage register corresponding to block Nos. 1 to 1024, and direction No. Dm is stored in a direction storage register corresponding to block Nos. 1 to 1024.
FIG. 39 and FIG. 40 are explanatory diagrams of detecting a ridge line direction in a conventional example. In FIG. 39, (A) shows a schematic view of a multivalued image of a pictured fingerprint, and (B) shows a schematic view of a binarized image obtained by binarizing the multivalued image. Based on the binarized image, detection in the ridge line direction on each block described above results in (C). Based on the result detected in the ridge line direction of each block, the multivalued image shown in (A) is subject to the above-described spatial filtering, and the result is shown in FIG. 40 (D). It is apparent by comparing the multivalued image of (D) and the multivalued image of FIG. 39 (A) that chapped portions are connected. Therefore, when the multivalued image of (D) is binarized, it is changed as shown in (E). When the binarized image of (E) is compared with the binarized image of FIG. 39 (B), it is apparent that the binarized image of (E) is clear.
In detecting the direction of ridge lines of a fingerprint in the conventional example, the direction of each picture element in the block is detected, the number of picture elements corresponding to the direction in the block is determined, and the direction that the number of picture elements becomes maximum is determined as the ridge line direction in the block. And, as to the directions that the number of picture elements is same, one of them is selected. Therefore, when the number of picture elements is same in directions which are intersecting at right angles and one of them is selected, there is a disadvantage of having a possibility that the direction becomes opposite from the flow of the ridge lines. In other words, there is a disadvantage that the ridge line direction not complying with the flow of the ridge lines of the peripheral blocks is detected.
For example, as shown in FIG. 41 (A), in the ridge line direction pattern of each block, when a ridge line direction not complying with the flow of the ridge lines of the peripheral blocks is obtained like a block indicated by 321, it is changed by the spatial filtering to a multivalued image which is schematically shown in (B), then it is converted into a binarized image which is schematically shown in (C), and a bridge is produced between the ridge lines at a portion indicated by 322 which corresponds to the block 321. Therefore, there is a disadvantage that an error occurs when minutiae are extracted.
And, a system has been put into practical use which checks a registered fingerprint with an affixed fingerprint, and if they match, unlocks a door to allow the entrance or allows to operate equipment. By checking fingerprints, security can be improved as compared with the use of a physical key. In such a case, it is necessary to manage the registered fingerprints with reliability and to prevent misuse such as alteration of the registered fingerprints.
FIG. 42 is an explanatory diagram of a fingerprint checking system, in which reference numeral 411 denotes a fingerprint checking device, 412 a fingerprint reading unit, 413 a control unit, 414 a storage unit for storing registered fingerprint data, 420 a host computer, 421 a processor (CPU), 422 a bus, 423 a random access memory (RAM), 424 a read-only memory (ROM) for storing data or the like, 425 a hard disk drive (HDD) for storing a large volume of registered fingerprint data, 425a registered fingerprint data, 425b a data destruction checking code, 426 and 427 an interface (IF), 430 a card reader, and 431 an IC card for keeping registered fingerprint data.
The host computer 420 can be a personal computer, and the hard disk drive 425, which is now relatively inexpensive and small, has a large capacity and can store a large volume of fingerprint data. The storage unit 414 in the fingerprint checking device 411 is a programmable read-only memory (EEPROM, flash memory, etc.) and can store registered fingerprint data for scores of people or several hundred people. And, if necessary, the registered fingerprint data stored in the hard disk device 425 in the host computer 420 can be downloaded to the storage unit 414.
To check fingerprints in the fingerprint checking device 411, an identification number (ID) is entered. To enter the identification number, a keyboard or a ten-key which is not illustrated can be used, or a medium such as an ID card which stores an identification number (ID) can be used. And, registered fingerprint data corresponding to the identification number is read from the storage unit 414, the registered fingerprint data is compared with the fingerprint data of an affixed fingerprint read by the fingerprint reading unit 412 by the control unit 413, and if they match, control of unlocking or the like is made according to an output signal from the control unit 413.
It is also possible to store the registered fingerprint data in the IC card 431. By reading the IC card 431 by the card reader 430, the registered fingerprint data can be transferred to the fingerprint checking device 411 through the host computer 420 and checked with data of an affixed fingerprint. The registered fingerprint data is configured by taking a picture of the affixed fingerprint, binarizing it, extracting a plurality of minutiae such as bifurcation points owing to the ridge lines of the fingerprint, determining each minutia as made of multiple picture elements, and using binarized data rows of the respective minutiae.
To check that data in a file having the registered fingerprint data is not destroyed, the data destruction checking code 425b is added to the registered fingerprint data 425a. By this data destruction checking code 425b, a total value, exclusive-OR or scrambled value of generating polynominal is used for all data contained in the file, and if the data stored in the file is changed even by one bit, this one bit change can be detected based on the data destruction checking code 425b. But, if the contents of the file are totally exchanged, detection cannot be made.
As shown in FIG. 42, the registered fingerprint data is stored in the storage unit 414 of the fingerprint checking device 411, stored in the hard disk drive 425 in the host computer 420 connected to the fingerprint checking device 411, or stored in a medium such as the IC card 431 or an optical card using a magneto-optical record medium.
Where the registered fingerprint data is stored in the fingerprint checking device 411, and if it is exchanged with another fingerprint checking device having other fingerprints stored according to the identification number identical to the identification number (ID) stored in the formal fingerprint checking device, all operation on the system side is not different, the registered fingerprint data is exchanged, and if another fingerprint is affixed using the same identification number (ID) as before, checking results in matching.
Where the fingerprint data is stored in the hard disk derive 425 in the host computer 420, the data file in the hard disk drive can generally be operated freely. For example, the registered fingerprint data file can be replaced by another file having different data with the same file name. Therefore, if some person who is not formally registered attempts to register his or her fingerprint in another system and the registered fingerprint data is reloaded by such registered fingerprint data, a person who is not formally registered can use the system illegally.
Where the registered fingerprint data is stored in a portable medium such as an IC card or optical card, the registered fingerprint data can be reloaded, so that misuse can be made in the same way as described above.
Accordingly, it is thought to insert a key number with respect to respective registered fingerprint data. The key number is inserted at a given byte of the registered fingerprint data, the byte number and the key number are made confidential, and the key number is stored so that the formally registered persons are not revealed. Even if the registered fingerprint data is exchanged, misuse cannot be made because the key numbers of the formally registered persons are also changed. But, as shown in FIG. 43, if the same key number is used to repeatedly register fingerprints, registered fingerprint data A, B and C become different owing to the positional change of minutiae and change of data rows of minutiae.
Accordingly, when registered fingerprint data A, B and C are read from the registered fingerprint data storage file and checked, the key number at the x-th byte from the leading address of respective registered fingerprint data A, B and C matches, and other areas do not match because they have a random property. In other words, it can be identified that the x-th byte where matching is obtained is where the key number is inserted. Thus, the key number can be read from the registered fingerprint data of the formally registered persons, so that misuse can be made.
And, a fingerprint checking entrance/exit control system has been proposed to authenticate personal identification by checking fingerprints, thereby allowing the entrance to a predetermined room or the like. And, such a fingerprint checking entrance/exit control system is desired to have an improved fingerprint checking accuracy.
FIG. 44 is an explanatory diagram of a fingerprint checking entrance/exit control system, in which a host device 531, a plurality of gates 532-1 to 532-n, and a given number of fingerprint registering devices 537-1 to 537-m are connected by a line 533 of a local area network (LAN), the respective gates 532-1 to 532-n have fingerprint checking units 540-1 to 540-n and electric locks 541-1 to 541-n, an affixed fingerprint is checked with the registered fingerprints in the fingerprint checking unit, and when personal identification is authenticated, an unlocking signal is given to the electric lock to release it. And, reference numeral 534 denotes a fingerprint registering unit, 535 a control unit, 536 a printer for outputting a list of registered persons, a list of setting or the like, 538-1 to 538-m control units, and 539-1 to 539-m fingerprint registering units.
To register a fingerprint by the fingerprint registering units 534, 539-1 to 539-m, personal information containing entrance allowing information such as name, identification number, post and room number in which he or she wants to enter is entered. The personal information and registered fingerprint data are stored in a file (not shown) in the host device 531. And, the personal information and registered fingerprint data are downloaded to the gate in conformity with the entrance allowing information. In this case, desired registered fingerprint data can be downloaded according to the demand from the gate.
When personal identification is authenticated by checking the registered fingerprint data with the affixed fingerprint, it is known that the registered fingerprint data is renewed by the affixed fingerprint data, and the registered fingerprint data is controlled as if it is obtained by the latest fingerprint registering operation. And, it is known that when first and second registered fingerprint data are stored, the affixed fingerprint is checked with the first registered fingerprint data and personal identification cannot be authenticated, the affixed fingerprint is checked with the second registered fingerprint data, and if personal identification cannot be authenticated yet, it is determined as a mismatch; but if personal identification can be authenticated, the second registered fingerprint data is renewed by the affixed fingerprint data (e.g., Japanese Patent Laid-Open Publication No. Sho 63-301376). By such a method, the probability of authenticating personal identification by the second fingerprint checking is improved, and the registered fingerprint data is renewed when the personal identification is authenticated, so that the latest registered fingerprint data can be used to check fingerprints.
As described above, the fingerprint checking entrance/exit control system is generally provided with the fingerprint checking units 540-1 to 540-n in the respective gates 532-1 to 532-n to check the fingerprints in a distributed manner. Therefore, when the above-described registered fingerprint data is renewed at the respective gates 532-1 to 532-n, the registered fingerprint data at the gate with a high frequency of use becomes the latest fingerprint data, a mismatch of the renewed registered fingerprint data at the respective gates occurs depending on the frequency of use, and the accuracy of authenticating personal identification is variable depending on the gates.
And, the fingerprint data stored in the host device 531 is the first one at the time of registering the fingerprint, and when entering a room after a long period since the fingerprint was registered in a gate determined according to the entrance allowing information, the registered fingerprint data is downloaded from the host device 531. But, since the fingerprint data is not latest, it is highly possible that checking results in a mismatch. Since it is thought that the fingerprint is one and only and not variable, it is used to authenticate personal identification, but it changes to some extent, and a state of the fingerprint face or the fingerprinted position varies every time fingerprinting is made, but the fingerprint data at the time of registering fingerprints is not always optimum. Therefore, by using the affixed fingerprint data with the conditions according to which personal identification can be authenticated at every fingerprinting for the next time, the checking probability can be improved, but as described above, there is a disadvantage that the registered fingerprint data not renewed is remained in the host device 531.
And, a fingerprint checking device has been put in practical use which configures a file with the identification number entered at the registration of fingerprints and the registered fingerprint data corresponded, and checks the registered fingerprint data read from the file based on the identification number entered for checking fingerprints with the affixed fingerprint to authenticate personal identification. And, improvement of operability of such a fingerprint checking device is demanded.
A system is known to control entrance/exit by checking fingerprints, and to register a fingerprint, personal information such as identification number, name, post, attribute and desired room number is entered, and a fingerprint is affixed. And, to enter a room, identification number is entered into the fingerprint checking device, and a fingerprint is affixed. The fingerprint checking device reads the registered fingerprint data from a file according to the entered identification number, checks it with the affixed fingerprint to authenticate personal identification, and if personal identification can be authenticated, releases the electric lock of the door to allow to enter.
Identification numbers for various systems are allocated without overlapping. For example, when a single fingerprint checking device in the entrance/exit control system can register fingerprints for 480 persons, by providing 32 fingerprint checking devices, in other words, if there is 32 rooms, 15360 persons can register a fingerprint. And, to allocate the identification number to these 15360 persons without overlapping, at least five digits are required. And, a larger-scaled entrance/exit control system may need the identification number of six digits or more.
Therefore, to enter a room, an identification number of five digits or six digits must be entered into the fingerprint checking device. Even if a fingerprint can be checked in a short time, the entrance of an identification number takes a long time, and the fingerprint checking device for a room where entrance and exit are frequent is particularly poor in operability.
And, the fingerprint checking device checks the previously registered fingerprints with a newly affixed fingerprint to authenticate personal identification, and the registered fingerprint is made by storing an area containing respective minutiae corresponding to a plurality of minutiae in multivalued image data obtained from a pictured fingerprint into a registration file. And, the binarized image data obtained by picturing an affixed fingerprint at checking the fingerprint is compared with respective areas of the binarized image data containing the minutiae read from the registration file, and if areas in prescribed number or more match, it is determined as a match. Accordingly, to improve the fingerprint checking accuracy, it is demanded to register fingerprints having a desired accuracy.
The fingerprint has two minutiae of an ending point and a bifurcation point of ridge lines, and most of fingerprint checking devices store the minutiae as registration data in the registration file. For the fingerprint registration, the multivalued image data obtained by picturing an affixed fingerprint is binarized, the binarized image data is thinning-processed, the ridge lines thinning-processed are extracted with the ending points and the bifurcation points as the minutiae, the binarized image data areas are cut out according to coordinate information of the minutiae, and they are stored as the registered data in the registration file.
FIG. 45 is an explanatory diagram of a fingerprint checking device, in which reference numeral 601 denotes an affixed fingerprint image pickup unit, 602 a data processing unit, 603 a bus, 604 a processor (CPU), 605 an interface (IF), 606 a read-only memory (ROM) storing a program, 607 a multivalued image memory, 608 a binarized image memory, 609 a binarized image save memory, 610 a thinning-processed image memory, 611 a minutia list memory, and 612 a nonvolatile memory for registered data. The processor 604 controls the respective units connected through a bus 603 and has a function of processing the image data.
The affixed fingerprint image pickup unit 601 comprises a fingerprinting stand on which a fingerprint is affixed, a lighting source, a CCD camera, a display, and an input operation unit such as a ten-key which are unillustrated. To register a fingerprint, information of an ID number and a password and a fingerprint registering request are entered through the input operation unit, a fingerprint is affixed onto the fingerprinting stand, and the affixed fingerprint is pictured by the CCD camera. A signal of the fingerprint image pictured by the affixed fingerprint image pickup unit 601 is A/D converted by the interface 605 into multivalued image data.
The memories 607 to 611 in the data processing unit 607 are cleared by initializing. And, the multivalued image data which was A/D-converted by the interface 605 is written into the multivalued image memory 607, the multivalued image data in the multivalued image memory 607 is binarized by the data processing function of the processor 604 and written into the binarized image memory 608.
The binarized image data in the binarized image memory 608 is copied and saved into the binarized image data save memory 609. And, the content of the binarized image memory 608 is subjected to thinning processing. In other words, the ridge lines of the fingerprint are changed into thin lines. The thinning-processed image data is written into the thinning-processed image memory 610. Based on the thinning-processed image data in the thinning-processed image memory 610, the minutiae of the ending points and bifurcation points are extracted, and coordinate information of the minutiae is written into the minutia list memory 611. When the number of minutiae is a prescribed number or more, images of minutiae are cut out of the binarized image save memory and stored into the nonvolatile memory 612 for registration data together with an ID number and a password.
To check a fingerprint, an ID number and a password are entered through the input operation unit of the affixed fingerprint image pickup unit 601, the fingerprint is affixed, and it is pictured. The fingerprint image signal is stored in the multivalued image memory 607 as multivalued image data in the same way as registering a fingerprint. And, the processor 604 examines the entered ID number and password, and if normal, the registered fingerprints are read from the nonvolatile memory 612 for registering, and based on the registered fingerprint in an area containing the minutiae, checked with the entered fingerprint, and if the number of matched points is equal to or more than a prescribed number, it is determined that personal identification was authenticated.
FIG. 46 is an explanatory view of a binarized image of a fingerprint, which is obtained by digitizing the analog image signal of the affixed fingerprint pictured, the multivalued image data is temporarily stored in the multivalued image memory 607 as described above, and the multivalued image data is binarized. In the binarized image state, since it is not easy to extract the ending point a or the bifurcation point b, the ridge lines are changed into thin lines. FIG. 47 shows an image having thin lines, and the ending point a and the bifurcation point b can be extracted easily by processing with a processor.
If the fingerprint image in the affixed fingerprint state is not good, for example, if the ridge lines are seen in a separated form despite that the ridge lines in the binarized image are continuous as indicate by c in FIG. 48(A), when the minutiae are extracted after thinning processing, the extraction is made with such separated points as the ending points.
In this case, since the coordinates of the minutiae are close, it is known to delete the minutiae, which are close in a certain range or 0.5 mm or below, as pseudo minutiae from the minutia list. Thus, the minutiae due to the separated points of the ridge lines indicated by c in FIG. 48(A) are deleted as pseudo minutiae.
When such pseudo minutiae are deleted, normal minutiae are also deleted when they are mutually close, and the number of minutiae to be registered in the minutia list is decreased. When the binarized image of FIG. 48(A) is changed into thin lines and the minutiae are extracted, the minutiae more than the extracted number of minutiae of the relatively good binarized image as shown in FIG. 46 can be extracted, but when pseudo minutiae are deleted, the remaining minutiae are decreased, and a desired number of minutiae may not be obtained. In registering a fingerprint, a prescribed number or more of minutiae are required, so that the registering process may fail by the pseudo minutia deleting process, and registering is made again.
Accordingly, for a blurred fingerprint like the binarized image of the fingerprint as shown in FIG. 48(A), it is known to effect the spatial filtering to connect the minutiae of the ridge lines. As a result, the binarized image as shown in FIG. 48(B) is obtained. When the binarized image is changed into thin lines, the normal minutiae only remain, and minutiae in a prescribed number or more can be extracted.
For a blurred fingerprint, even when pseudo minutiae are deleted by the spatial filtering, the number of normal minutiae becomes a prescribed number or more, a failing possibility in the registering process is lowered, and as compared with a case of registering with the pseudo minutiae included, the checking rate in fingerprint checking is improved. But, when the fingerprint image has good quality and the spatial filtering is made, a possibility of converting the pseudo minutiae into the normal minutiae is high.
For example, the binarized image of the fingerprint shown in FIG. 49(A) has relatively good quality, and when the spatial filtering is made when there is a crack as indicated by d, the binarized image shown in (B) is obtained, the crack indicated by d in (A) is converted into a normal minutia as indicated by e in (B) and registered.
FIG. 50(A) shows a multivalued image of a fingerprint having large cracks, and (B) shows a multivalued image which has through the spatial filtering, and f shows a state that cracks have continued. And, when a fingerprint is checked, the spatial filtering is not applied to the fingerprint image data to check with the registered fingerprints, and the match rate of the fingerprint is high when the normal minutiae having a crack are registered than when the pseudo minutiae are registered, and it becomes higher when the normal minutiae without any crack are registered. In other words, there are cases that the match rate of fingerprints can be improved by the spatial filter processing and the match rate cannot be improved.